Research Description

I am interested in testing basic ecological and evolutionary processes occurring within plants and their associated fungi. Much of the conceptual basis of ecology and evolution was developed with animals in mind. Plants and fungi differ from animals in important ways, including their motility, their nutrient acquisition systems and their genetic systems. Conceptual frameworks building on these peculiarities can be very useful in exploring the dynamics of populations and communities of plants and fungi. Developing, testing, and exploring the implications of these models and has been the goal of my work.

Maintenance of Diversity in Plant Communities

We have found that dynamics within the soil community can be a major driver of dynamics within the plant community. The presence of a particular plant host changes the composition of the soil community and the change in soil community composition often decreases the growth rate of their host plant. Through this negative feedback on plant growth, the dynamics within the soil community can directly contribute to the maintenance of diversity within plant communities and populations. We have found that these negative feedbacks can result from accumulation of host-specific soil pathogens, specifically fungal pathogens in the genus Pythium. However, host-specific shifts in the composition of mutualistic mycorrhizal fungi and of soil bacteria also generate these feedbacks.

Ecology of Arbuscular Mycorrhizal Fungi

We have been particularly interested in the ecological and evolutionary dynamics between plants and their mutualistic mycorrhizal fungi. The roots of most plant species form symbiotic associations with arbuscular mycorrhizal fungi, which facilitate their uptake of soil minerals. We have found communities of AM fungi to be very diverse and that individual fungal species are ecologically distinct. We are accumulating evidence that the dynamics and diversity within the AM fungal community can play an important role in determining the diversity and composition of plant communities.

Restoration of Native Plant Diversity after Disturbance

The original tallgrass prairie that dominated the Midwest was fantastically diverse. Unfortunately, much of this community type has been lost due to agricultural development. Efforts to replant agricultural fields into prairie have met some success, but the original diversity has not been restored. We are evaluating whether the degradation of the soil community, particularly the community of mycorrhizal fungi, limits the success of restorations. We find support for an important role of native mycorrhizal fungi and find that restoration of this native diversity can have cascading benefits for ecosystem functions, including reduced erosion.

Genetics of Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhizal fungi are thought to reproduce solely through the asexual processes of hyphal growth and production of asexual spores. However, we have found substantial amounts of heritable variation within single populations of these fungi. In culturing these fungi, we have found evidence of an unusual mechanism of inheritance within these fungi in which variable nuclei segregate through dividing and growing hyphae. New combinations of nuclei can then be created through hyphal fusion. We are developing and testing the implications of these genetic processes.

Evolution of Mutualism within the Plant-AM fungal Interaction

The evolution of mutualism between plants and their belowground symbionts is not adequately explained by current evolutionary theory. Because the delivery of benefit to the host likely involves some cost to the symbiont, symbionts that provide reduced benefit to their host would be expected to increase in frequency, leading to the dissolution of the mutualism. We have demonstrated this expected decline in mutualism in our observation of negative feedback on plant growth through changes in the composition of the mycorrhizal mutualism. The processes that might prevent the dissolution of the mutualism has been an unresolved question in evolutionary ecology. We have identified the conditions through which plants can influence the direction of evolution in their symbionts through preferential allocation. We have used carbon labeling experiments to demonstrate preferential allocation to the more mutualistic fungi and have found that this preferential allocation results in increased fitness of the more mutualistic fungi provided there is sufficient spatial structure.

Other Topics of Interest

Students in our lab are addressing a diversity of issues within ecology and evolution, including interspecific competition among AM fungi, AM fungal systematics, ecology of multitrophic interactions, factors affecting plant community invasibility, evolution of virulence in microbial pathogens, and the evolution of plant dependence on mycorrhizal fungi.